Crystal oscillator circuits use the mechanical resonance of a vibrating crystal of piezoelectric material to create an electrical signal with a precise frequency. This frequency may be used to keep track of time (as in quartz wristwatches), to provide a stable clock signal for digital integrated circuits or systems on a chip, and to stabilize frequencies for radio transmitters and receivers. However, the motional resistance of the crystal, also called the equivalent series resistance, results in undesirable electrical losses.
These crystal oscillator circuits provide a small amplitude output signal. In order to convert this small amplitude output signal to a full swing output signal, an inverter stage may be utilized. A conventional inverter stage used for these purposes employs, among other components, a PMOS transistor and an NMOS coupled in series between a supply and ground and controlled by the input to the inverter stage such that when the input makes a transition, for a certain range of input voltage both the PMOS transistor and the NMOS transistor are undesirably on. When both the PMOS transistor and the NMOS transistor are on simultaneously, current undesirably flows from the supply to ground, which increases the losses of the inverter stage, and thus the circuit using both the crystal oscillator circuit and the inverter stage.
Mobile devices may employ the crystal oscillator circuits described above as well as the inverter stages described above. In mobile devices that operate based on battery power, reducing electrical losses is highly desirable. Consequently, circuits able to compensate such crystal oscillators for losses are desirable, as well as circuits able to compensate such inverter stages for losses.